1. Field of the Invention
The present invention relates to a process for preparing a conductive, acicular zinc oxide. More particularly, the present invention is concerned with a process for preparing an acicular zinc oxide which has an improved conductivity while maintaining the whiteness on a high level and is useful as a pigment to be blended into a coating composition, a resin, a rubber and a fiber in applications where electrification and static charge buildup must be prevented.
2. Prior Art
Zinc oxide is useful as a pigment to be blended into a coating composition, a resin, a rubber and a fiber, and especially a zinc oxide having excellent conductivity has been desired in applications where electrification and static charge buildup must be prevented. Among such zinc oxides, those in a non-branched acicular form (needle-like) or in a branched acicular form (tetrapod-like) (hereinafter collectively referred to as an acicular zinc oxide) are superior to a granular zinc oxide in that a conductivity network is created by the addition thereof in a small amount. Accordingly, a zinc oxide which is not only high in conductivity but also acicular has been desired in the art.
Japanese Patent Application Laid-Open Gazette No. (Hei.)3-28125 (28125/1991) discloses a process developed by the present inventors for preparing an acicular, conductive zinc oxide. This process comprises neutralizing a solution containing an alkali zincate compound and a salt of a specific metal, such as aluminum, with a mineral acid to obtain precipitates, and subjecting the precipitates to dehydration and firing in a reducing atmosphere. The acicular, conductive zinc oxide obtained by such process has fairly good characteristics, but this process has a problem in productivity, because a large amount of alkali is required to keep zinc dissolved and a large amount of acid is required to neutralize the solution. Further, in this process, it is difficult to impart conductivity to the acicular zinc oxide previously prepared by conventional processes, such as the dry process and the wet process.
Japanese Patent Application Laid-Open Gazette No. (Hei.)3-60429 (60429/1991) discloses another process for preparing a conductive, acicular zinc oxide. This process comprises adding an aqueous solution of ammonium carbonate and an aqueous solution of aluminum sulfate to a dispersion of an acicular zinc oxide, followed by stirring for a predetermined period of time and dehydration and firing in a reducing atmosphere. However, the conductive, acicular zinc oxide prepared by this process has conductivity and whiteness which are both unsatisfactory, and hence further improvement has been desired.